1. Field of the Invention
The present invention relates to a polyelectrolyte, a membrane electrode assembly, a fuel cell, and a method for producing a polyelectrolyte. The invention especially relates to a polyelectrolyte, a membrane electrode assembly, a fuel cell, and a method for producing a polyelectrolyte for polymer electrolyte fuel cells.
The invention is applicable to polymer electrolyte fuel cells for use in electric vehicles, cellular phones, vending machines, underwater robots, submarines, spacecrafts, underwater vehicles, power supplies for underwater bases, etc.
2. Description of the Related Art
In recent years, fuel cells have received attention as an effective solution of environmental problems and energy problems. A fuel cell oxidizes hydrogen or a like fuel using oxygen or a like oxidizer, and converts the thus-generated chemical energy into electrical energy.
According to the kind of electrolyte, fuel cells are classified into an alkali type, a phosphoric acid type, a polymer electrolyte type, a fused carbonate type, a solid oxide type, etc. Polymer electrolyte fuel cells (PEFC) are designed for low-temperature operation with high power density, and thus can be reduced in size and weight. For this reason, they are expected to be applied to portable power supplies, household power supplies, and in-car power sources.
Perfluoro electrolytes, such as practically stable Nafion (registered trademark), and various hydrocarbon electrolytes are used as electrolytes for polymer electrolyte fuel cells (PEFC). However, although these electrolytes have high proton conductivity, there is a problem that the cost therefor is high.
In order to solve the above problem, use of inexpensive hydrocarbon electrolytes has been considered. However, although these electrolytes have high proton conductivity, there is a problem that they lack practical stability (durability).
In order to solve this problem, improvement of durability by complexation of an electrolyte and a radical-quenching material (antioxidant) has been considered (see JP-A-2006-269357 and JP-A-2007-66882).
However, when a radical-quenching material is simply added to an electrolyte, the radical-quenching material is eluted out of the electrolyte during operation of the fuel cell, and consequently the radical-quenching material does not work sufficiently. For the purpose of preventing the elution, addition of a high-molecular-weight radical-quenching material has also been considered. However, because of its high molecular weight, highly dispersion thereof in an electrolyte is impossible. Accordingly, also in this case, the radical-quenching material does not work sufficiently.